Wireless communication systems support and provide a wide variety of features and functions for their users. For example, conventional voice/data systems allow a subscriber/mobile station to monitor multiple communication channels provided by the fixed network equipment for traffic that is of concern to that mobile station. This is typically referred to as the mobile station being in “scan mode.” Scan mode allows a mobile station to check a succession of radio channels on a periodic basis to determine if voice information is present, and then to remain on that channel to receive the voice information. At times, this means that the mobile station will arrive on the channel in mid-transmission.
Transmitted voice, whether sent in analog or digital form, is designed to readily allow a late entry into the transmission through the periodic inclusion in the voice transmission of synchronization (sync) and destination ID information. The periodic inclusion of this information permits the mobile station to determine that the voice information is intended for that station, and allows the mobile station to receive the subsequently transmitted, although incomplete information.
An enhanced form of scan mode is referred to as priority scan. In priority scan the user may designate certain channels, typically 1 or 2 channels, as priority channels. These channels are scanned more frequently, usually every other channel as the mobile station advances through its scan channels list. Moreover, if the mobile station is receiving a transmission on a non-priority channel, it will, during reception, scan to the priority channels on a periodic basis. This act of scanning interrupts the transmission on the non-priority channel for the duration of the priority scan cycle.
Incomplete reception of data information, and more particularly a data packet, will result in an error for the entire data packet. In part, this is due to the fact that data packets are fairly short in duration and include sync and destination information only at the beginning of the packet. If the sync and destination information are not received, the content of the data packet cannot be received. In addition, outbound data packets are unsolicited, asynchronous events so the mobile station has no way of knowing when or on what channel a data packet will arrive. The act of changing frequencies is bound to leave the mobile station on either the wrong frequency or arriving on the correct frequency in the middle of the data packet, thus resulting in an error in reception of the data packet. The effect is missed packets and an avalanche of retries developing in the system. The increasing number of retries cause a reduction in the available capacity for the data that the system is attempting to send. Priority scan exacerbates the problem by almost assuring that data packets will be interrupted or not received entirely.
Because of these problems with receiving data information while the mobile station is in either scan mode or priority scan, in some instances the availability of scan mode and priority scan has been limited to those users who do not require data reception. Alternatively, to allow both scan mode and data reception, a lengthy preamble is inserted in front of each data packet sent within the system. The lengthy preamble increases the probability that when the scanning mobile station arrives on a channel, a portion of the preamble is still present. The mobile station detects the preamble and remains on the channel to receive the data packet. However, in such an arrangement, the preamble must be as long as the time necessary to complete the scan sequence. The scan sequence may be several seconds in length. Thus, the preamble would have to be several seconds in duration, which in most cases will be many many times the length of the data packet being transmitted. The direct result is that the amount of information that can be carried on the channel is greatly reduced.
Thus, there is a need for a method and apparatus for permitting scan mode and priority scan with data reception in an integrated voice/data communication system without significantly degrading the information carrying capacity of the communication channel.